Pen cap



FIG. 1 is a top plan view of the pen cap showing my new design;

FIG. 2 is the bottom plan view of the pen cap;

FIG. 3 is the rear elevational view of the pen cap;

FIG. 4 is the left elevational view of the pen cap; the right side being a mirror image thereof; and,

FIG. 5 is the front elevational view of the pen cap. 

The ornamental design for a pen cap, as shown and described. 